In metal fabrication it is often necessary to fasten adjacent sheets of metal such as the webs of steel purlins or the overlapping junction of two cladding sheets in a steel frame system. Typically fine threaded screws of constant pitch and gauge are used since a fine thread is required to draw the two sections together tightly when the screw is fully wound into the aligned guide holes drilled in the two sections.
A course threaded screw would not bring the sections closely together since the coarse thread allows separation of the sections even in the fully tightened configuration. In fact the pitch of the thread required to bring the sections together tightly is approximately equal to the thickness of the sections.
However a fine threaded screw requires many rotations to achieve full insertion, in fact one rotation for each of the threads of the screw. Further since the guide holes have a diameter somewhat less than the screw, the guide holes need to be in close alignment for insertion to start and considerable driving force is required to complete insertion. Accordingly the fastening of metal sections using such fine threaded screws is problematic and time consuming.
Clearly it would be advantageous to provide a fastener for securing metal sheets in a steel frame system which is easy to insert in guide holes and fast to drive, or at least provides an alternative to existing fasteners.